This invention relates to a cyclone separator and, more particularly, to such a separator for separating solid particles from gases discharged from a fluidized bed combustion system.
Fluidized bed reactors, usually in the form of combustors, boilers, gasifiers, or steam generators, are well known. In a normal fluidized bed arrangement, air is passed through a perforated plate, or grate, which supports a bed of particulate material, usually including a mixture of fuel material, such as high sulfur bituminous coal, and an absorbent material for the sulfur released as a result of the combustion of the coal. As a result of the air passing through the bed, the bed behaves like a boiling liquid which promotes the combustion of the fuel. In addition to considerably reducing the amount of sulfur-containing gases introduced to the atmosphere, such an arrangement permits relatively high heat transfer rates per unit size, substantially uniform bed temperatures, relatively low combustion temperatures, and reduction in corrosion and boiler fouling.
In the fluidized bed combustion process, the fluidizing air, after passing through the bed, combines with the products of combustion and rises above the level of the fluidized bed to a freeboard area, and in so doing, entrains a substantial amount of relatively fine solid particles from the fluidized bed. Of the various techniques that have evolved for separating the entrained solid particles from the mixture of air and gases, the cyclone separator is the most popular. In these arrangements the mixture of air and gases with the entrained particles are swirled in an annular chamber to separate the particles from the mixture by centrifugal forces.
Conventional cyclone separators are normally provided with a monolithic external refractory wall which is abrasion resistant and insulative so that the outer casing runs relatively cool. Typically, the wall of a conventional separator is formed by an insulative refractory material sandwiched between an inner hard refractory material and an outer metal casing. In order to achieve proper insulation, the thickness of these layers must be relatively large which adds to the bulk, weight, and cost of the separator. Also, the outside metal casing cannot be further insulated from the outside since to do so could raise its temperature as high as 1500.degree. F. which is far in excess of the maximum temperature it can tolerate. Further, most conventional cyclone separators require relatively expensive, high temperature, refractory-lined ductwork and expansion joints between the reactor and the cyclone, and between the cyclone and the heat recovery section, which are fairly sophisticated and expensive. Still further, conventional separators formed in the above manner require a relatively long time to heat up before going online to eliminate premature cracking of the refractory walls. This, of course, is inconvenient and adds to the cost of the process.